In principle, a satellite should remain capable of maneuvering up to the end of its provided operating life to the extent possible. This is, however, no longer the case, when the propellant is completely used up. Therefore, the satellite must be taken out of operation in a controlled manner, as long as propellant is still available. In satellites the problem exists, however, that in a later operational phase it can no longer be exactly determined how much propellant is still located in the tank, because standard methods, such as weighing, do not function in zero gravity conditions. Moreover, for propellants with a liquid phase, the remaining or residual quantity can also not be measured via the pressure of the gas phase, because the gas phase pressure does not exist according to a fixed relation to the volume or the mass of the liquid phase. Finally, the remaining propellant also cannot always be determined from the difference between the original tank filling and the propellant that has flowed out in the course of the operation of the satellite via a throughflow measurement, because the latter also becomes less accurate over time. Therefore, for safety reasons the deployment duration of a satellite is often already ended before all of the propellant has actually been used up.
The determination of the propellant or fuel quantity in propellant or fuel tanks with the aid of radiometric auxiliary means is already known according to the patent documents U.S. Pat. No. 3,501,632 A and U.S. Pat. No. 4,755,677 A. Besides that, an arrangement of the initially mentioned type with scintillation fiber bundles extending along the container wall has become known for fill level measurement from the patent documents U.S. Pat. No. 4,471,223 A, DE 10 2008 011 382 A1 and DE 699 07 659 T2 as well as once again from U.S. Pat. No. 3,501,632 A. Finally, the patent documents US 2012/0020457 A1, U.S. Pat. No. 4,471,223 A and DE 10 2008 011 382 A respectively describe arrangements of a gamma radiation emitter in the center of a tank, and U.S. Pat. No. 3,531,638 A describes the reversed arrangement of a detector in the center of such a tank.